Low-dialectric polyimide film and method for producing same

ABSTRACT

Disclosed herein is provided a method for manufacturing a polyimide film, the method comprising the steps of: preparing a polyamic acid solution; preparing a polyamic add composition by adding 2-3 mole equivalents of a dehydrating agent to the polyamic acid solution; and applying the polyamic acid to a support to form a film, followed by thermosetting the film in a heater.

TECHNICAL FELD

The present disclosure relates to a polyimide film having highheat-resistance, low dielectric, and low optical transmittanceproperties in combination and a manufacturing method therefor.

BACKGROUND ART

Polyimide (PI), based on highly chemically stable imide rings in arobust aromatic backbone, is a polymeric material that has the highestlevels of heat resistance, drug resistance, electric insulation,chemical resistance, and weather resistance among organic materials.

Particularly, with their excellent insulation properties (i.e.,excellent electric properties such as low dielectric constants),polyimides enjoy applications as high-performance polymers in diversefields including electric, electronic, and optical fields.

Recently, flexible, thin-film circuit boards with a high degree ofintegration have been actively developed with the weight reduction andminiaturization of electronics.

Thin-film circuit boards tend to take advantage of a structure in whicha circuit including a metal foil is formed on a highly flexiblepolyimide film with excellent heat resistance, low-temperatureresistance, and insulation properties.

In such thin-film circuit boards, flexible metal-dad laminatespredominate, as exemplified by a flexible copper dad laminate (FCCL) inwhich a thin copper sheet is used as a metal foil. In this regard,polyimide is employed as a protection film, an insulation film, and soon in thin film circuit boards.

With the installation of various functions therein, electronic deviceshave recently been required to have fast calculation and communicationspeeds. To meet this requirement, development has been made of thin-filmcircuit boards that enable high-speed communication at a high frequency.

Realization of high-speed communication at high frequency requires aninsulator with a high impedance that allows for the maintenance ofelectrical insulation even at high frequencies. With the relationship ofinverse proportion of an impedance to the frequency and dielectricconstant (Dk) formed in an insulator, as low a dielectric constant aspossible is advantageous for maintaining insulation at high frequencies.

As for general polyimides, however, their dielectric properties fallshort of a level excellent enough to maintain sufficient insulation inhigh-frequency communication.

In addition, it has been reported that insulators with lower dielectricproperties are more likely to reduce undesired stray capacitance andnoise generation in a thin-film circuit board, thereby significantlyremoving causes of communication latency.

Accordingly, a polyimide with low-dielectric properties is now acceptedas an important factor above all else in the performance of a thin-filmcircuit board.

In the case of high-frequency communication, dielectric dissipationthrough polyimide inevitably occurs. Since dielectric dissipation factor(Df), which is a degree of electrical energy loss in a thin-film circuitboard, closely correlates with the signal propagation delay thatdetermines communication speed, maintenance of the dielectricdissipation factor at as low a level as possible is recognized as animportant factor for the performance of a thin-film circuit board.

A polyimide film with a higher moisture content is more apt to increasein dielectric constant and dielectric dissipation factor. With excellentintrinsic properties, polyimide films are suitable as materials forthin-film circuit boards. However, polyimide films may be relativelyvulnerable to moisture due to the imide groups with polarity and assuch, may be decreased in insulation properties.

Therefore, there is a need for developing a polyimide film that retainscertain levels of characteristic mechanical, thermal, low-opticaltransmittance, and anti-chemical properties thereof and shows dielectricproperties, particularly, a low-dielectric dissipation factor.

DISCLOSURE Technical Problem

Provided to solve the problems are a polyimide film having lowdielectric, low hygroscopic, and low optical transmittance properties incombination and a manufacturing method therefor.

To this end, the present disclosure substantially aims to provideexemplary embodiments.

Technical Solution

To accomplish the aims, an aspect of the present discourse provides amethod for manufacturing a polyimide film, the method including thesteps of:

preparing a polyamic acid solution;

preparing a polyamic acid composition by adding 2-3 mole equivalents ofa dehydrating agent to the polyamic acid solution; and

applying the polyamic acid to a support to form a film, followed bythermosetting the film in a heater.

In the step of preparing a polyamic acid composition, an imidizingcatalyst may be additionally added in an amount of 0.5-2 moleequivalents to the polyamic acid solution.

The polyamic acid solution may contain an acid dianhydride componentincluding 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), andpyromellitic dianhydride (PMDA) and a diamine component includingm-tolidine, 4,4′-oxydianiline (ODA), and p-phenylenediamine (PPD).

Based on a total of 100% by mole of the acid dianhydride component,3,3′,4,4′-biphenyltetracarboxylic dianhydride may be used at a contentof 30% by mole to 50% by mole and pyromellitic dianhydride may be usedat a content of 50% by mole to 70% by mole.

Based on a total of 100% by mole of the diamine component, m-tolidinemay be used at a content of 60% by mole to 80% by mole for,p-phenylenediamine may be used at a content of from 10% by mole to 25%by mole, and 4,4′-oxydianiline (ODA) may be used at a content of from10% by mole to 25% by mole.

The dehydrating agent may be an acetic anhydride and the imidizingcatalyst may be at least one selected from the group consisting ofisoquinoline, S-picoline, pyridine, imidazole, 2-imidazole,1,2-dimethylimidazole, 2-phenylimidazole, and benzimidazole.

In the thermosetting step, the thermosetting may be carried out at450-520° C. for 3 minutes (exclusive) to 6 minutes (inclusive).

The polyimide film may include a copolymer composed of two or moreblocks.

Another aspect of the present disclosure provides a polyimide filmmanufactured by the manufacturing method.

The polyimide film may have a moisture absorption rate of 0.3% or lessand a dielectric dissipation factor (Df) of 0.003 or less.

In addition, the polyimide film may have an optical transmittance of 25%or less.

A further aspect of the present disclosure provides a multilayer filmincluding the polyimide film and a plastic resin layer, and a flexiblemetal clad laminate including the polyimide film and anelectroconductive metal foil.

A yet further aspect of the present disclosure provides an electronicpart comprising the flexible metal dad laminate.

Advantageous Effects

As stated in the foregoing, the polyimide film comprising specificcomponents at specific ratios, manufactured by the method of the presentdisclosure, exhibits low dielectric, low hygroscopic, and low opticaltransmittance properties in combination, thus finding applications invarious fields demanding such properties, especially, electronic partssuch as flexible metal-dad laminates, etc.

BEST MODE FOR CARRYING OUT THE INVENTION

Below, a detailed description will be given of the present disclosure inthe order of “method for manufacturing a polyimide film” and “polyimidefilm”.

Terms and words used in the present specification and claims should notbe limited to general or dictionary meanings, but are to be construed asmeanings and concepts meeting the technical ideas of the presentdisclosure based on a principle that the present inventors mayappropriately define the concepts of terms in order to describe theirinventions in the best mode.

Therefore, the configurations of embodiments described herein are onlyone of the most preferred embodiments of the present disclosure and donot represent all the technical spirits of the present disclosure. Thus,it should be understood that there may be various equivalents andmodification examples that can replace them at the time of filing thepresent application.

Singular forms as used herein include plural forms unless the contextclearly indicates otherwise. It should be understood that the term“comprise”, “includes”, or “have”, etc., as used herein specifies thepresence of implemented features, numerals, steps, components, or acombination thereof, but does not preclude the presence or addition ofone or more other features, numerals, steps, components, or acombination thereof.

It should be understood that when an amount, concentration, or othervalue or parameter as used herein is given as an enumeration of a range,a preferable range, or preferable upper and lower values, all rangesformed with any upper limit or preferable values of any one pair and anylower limit or preferable values of any one pair are specificallydisclosed, regardless of whether the range is disclosed separately.

When a range of numerical values is referred to herein, the range isintended to include endpoints thereof and all integers and fractionswithin that range, unless stated otherwise. It is intended that thescope of the present disclosure is not limited to specific valuesrecited when the range is defined.

As used herein, the term “acid dianhydride” is intended to encompassprecursors or derivatives thereof which may not fall within the scope ofdianhydrides from a point of technical view, but nevertheless will reactwith diamine to form polyamic acids which can be then converted intopolyimides.

As used herein, the term “diamine” is intended to encompass precursorsor derivatives thereof which may not fall within the scope of diaminesfrom a point of technical view, but nevertheless will react withdianhydride to form polyamic acids which can be then converted intopolyimides.

A method for manufacturing a polyimide film according to the presentdisclosure comprises the steps of: preparing a polyamic acid solution;preparing a polyamic acid composition by adding 2-3 mole equivalents ofa dehydrating agent to the polyamic acid solution; and applying thepolyamic acid to a support to form a film, followed by thermosetting thefilm in a heater.

In the present disclosure, the preparation of a polyamic acid may beachieved by

(1) a method in which polymerization is carried out by adding the entireamount of a diamine component to a solvent and then a substantiallyequimolar amount of an acid dianhydride component,

(2) a method in which the polymerization is carried out by adding theentire amount of an acid dianhydride component to a solvent and then asubstantially equimolar amount of a diamine component,

(3) a method in which the polymerization is carried out by: adding someof a diamine component to a solvent; mixing some of an acid dianhydridecomponent at a ratio of about 95-105% by mole relative to the reactioncomponent; and adding the residual diamine component and subsequentlythe residual acid dianhydride component to make the respective amountsthe diamine component and the acid dianhydride component substantiallyequimolar,

(4) a method in which the polymerization is carried out by: adding anacid dianhydride component to an organic solvent; mixing some of adiamine component at a ratio of 95-105% by mole relative to the reactioncomponent; and adding a different acid dianhydride component andsubsequently the residual diamine component to make a total of theamounts of the acid dianhydride components substantially equimolar tothe total amount of the diamine component, or

(5) a method in which the polymerization is carried out by: reactingsome of a diamine component with some of an acid dianhydride componentin a solvent where any one of the diamine component and the aciddianhydride component is used in excess to form a first composition;reacting some of the diamine component with some of the acid dianhydridecomponent in a different solvent where any one of the diamine componentand the acid dianhydride component is used in excess to form a secondcomposition; and mixing the first and the second composition, whereinwhen the first composition is formed by using the diamine component inexcess, the second composition is formed by using the dianhydride inexcess or when the first composition is formed by using the aciddianhydride component in excess, the second composition is formed byusing the diamine component in excess, whereby the total amount of thediamine component is substantially equimolar to the total amount of theacid dianhydride component.

However, the polymerization method is not limited to those given above,the first to the third polyamic acid maybe prepared using any methodknown in the art.

A polyimide film may be manufactured using a thermal imidizationprocess, a chemical imidization process, or a composite imidizationprocess employing thermal and chemical imidization in combination.

As used herein, the term “thermal imidization process” refers to aprocess in which an imidization reaction is induced using a heat source,such as hot wind or an infrared dryer, without a chemical catalyst.

According to a thermal imidization process, the gel film is thermallytreated at temperatures varying from 100 to 600° C. to imidize amic acidgroups present in the gel film, particularly at temperatures from 200 to500° C., and more particularly at temperatures from 300 to 500° C.

According to a thermal imidization process, the gel film is thermallytreated at temperatures varying from 100 to 600° C. to imidize amic acidgroups present in the gel film, particularly at temperatures from 200 to500° C., and more particularly at temperatures from 300 to 500° C.

During the formation of the gel film, the amic acid groups may beimidized in part (about 0.1 to 10% by mole). In this regard, thepolyamic add composition may be dried at temperatures varying from 50°C. to 200° C. This process may also fall within the scope of the thermalimidization process.

For a chemical imidization process for manufacture of a polyimide film,a dehydrating agent and an imidizing agent are employed according to amethod known in the art.

In the present disclosure, the polyimide film may be manufactured by acomposite imidization process in which a dehydrating agent and animidizing catalyst is added to a polyamic acid solution which is thenheated to afford a polyimide.

When the dehydrating agent is added at less than 2 molar equivalents inthe polyimide film manufacturing method of the present disclosure, thefilm is difficult to form. More than 3 molar equivalent of thedehydrating agent increases dielectric dissipation factor, moistureabsorption rate, and optical transmittance values, which are far fromaway the desired low dielectric, low moisture absorption, and lowoptical transmittance properties for the polyimide film.

In the step of preparing a polyamic composition, 0.5-2 molar equivalentsof an imidizing catalyst may be additionally added to the polyamic acidsolution.

The dehydrating agent functions to dehydrate a polyamide acid to inducering closure as exemplified by aliphatic acid anhydride, aromatic acidanhydrides, N,N′-dialkyl carbodiimide, lower aliphatic halides,halogenated lower aliphatic acid anhydrides, arylsulfonic aciddihalides, thionyl halides, etc.

Particularly preferred is acetic anhydride.

Examples of the imidizing catalyst include aliphatic tertiary amines,aromatic tertiary amines, and heterocylic tertiary amines. So long as itis a component which accelerates the dehydrating and ring-closing effectof the dehydrating agent on the polyamide acid, any catalyst may beused.

Among others, the imidizing catalyst is preferably at least one selectedfrom the group consisting of isoquinoline, β-picoline, pyridine,imidazole, 2-imidazole, 1,2-dimethylimidazole, 2-phenylimidazole, andbenzimidazole.

In the method for manufacturing a polyimide film according to thepresent disclosure, the polyamic acid solution may contain an adddianhydride component including 3,3′,4,4′-biphenyltetracarboxylicanhydride (BPDA) and pyromellitic dianhydride (PMDA), and a diaminecomponent including m-tolidine, 4,4′-oxydianiline (ODA), andpara-phenylene diamine (PPD).

In some embodiments, the content of 3,3′,4,4′-biphenyltetracarboxylicanhydride may be in the range of 30% by mole to 50% by mole and thecontent of pyromellitic dianhydride may be in the range of 50% by moleto 70% by mole, based on a total of 100% by mole of the acid dianhydridecomponent.

In some particular embodiments, a content may be set forth to range from35% by mole to 45% by mole for the 3,3′,4,4′-biphenyltetracarboxylicanhydride and from 55% by mole to 65% by mole for the pyromelliticdianhydride, based on a total of 100% by mole of the acid dianhydride.

In some embodiments, the content of m-tolidine may be in the range of60% by mole to 80% by mole and the content of para-phenylene diamine maybe in the range of from 10% by mole to 25% mole, and the content of4,4′-oxydianiline may be in the range of 10% by mole to 25% by mole,based on a total of 100% by mole of the diamine component.

In some particular embodiments, a content may be set forth to range from65% by mole to 75% by mole for m-tolidine, from 10% by mole to 20% bymole for the para-phenylene diamine, and from 10% by mole to 20% by molefor the 4,4′-oxydianiline, based on a total of 100% by mole of thediamine component.

In the present disclosure, the polyimide chain derived from3,3′,4,4′-biphenyltetracarboxylic dianhydride has the structure ofso-called charge transfer complex (CTC), that is, an ordered linearstructure in which electron donors and electron acceptors are positionedin proximity to each other, with an intermolecular interaction enhancedtherebetween.

Being effective of preventing the formation of hydrogen bonds withmoisture, such a structure has a decreasing influence on moistureabsorption rate and as such, can bring about a maximum effect ofdecreasing the hygroscopic property of the polyimide film.

In some particular embodiments, the polyamic acid solution may furthercontain pyromellitic dianhydride as a dianhydride component. As adianhydride component with a relatively stout structure, pyromelliticdianhydride may be preferred due to conferring proper resilience on thepolyimide film.

For the polyimide film to meet pertinence in terms of both resilienceand moisture absorption rate, the content ratio of the dianhydrides isparticularly important. For instance, a lower content ratio of3,3′,4,4′-biphenyltetracarboxylic dianhydride makes it more difficult toachieve a low moisture absorption rate due to the CTC structure.

The aromatic moiety of the acid dianhydride component is accounted forby two benzene rings in 3,3′,4,4′-biphenyltetracarboxylic dianhydride,but by one benzene ring in pyromellitic dianhydride.

In the acid dianhydride component, an increase in the content ofpyromellitic dianhydride is construed to be an increase in the number ofimide groups within the molecule in view of the same molecular weight,indicating that the proportion of the imide group derived frompyromellitic dianhydride in the polyimide chain is relatively increased,compared to that of the imide group derived from3,3′,4,4′-biphenyltetracarboxylic dianhydride.

Accordingly, an increased content of pyromellitic dianhydride is alsounderstood as a relative increase of the imide group in the entirepolyimide film, leading to difficulty in expecting low moistureabsorption rates.

In contrast, a reduced content of pyromellitic dianhydride accounts fora relative reduction in a component responsible for the stout structureand thus may decrease the mechanical properties of the polyimide to anundesirable level.

For this reason, when contents of 3,3′,4,4′-biphenyltetracarboxylicdianhydride exceed the upper limits of the ranges set forth abovetherefor, the polyimide film has degraded mechanical properties andcannot attain heat resistance at a level sufficient to manufacture aflexible metal clad laminate.

When 3,3′,4,4′-biphenyltetracarboxylic dianhydride is used at contentslower than the lower limits of the ranges set respectively forththerefor or when pyromellitic dianhydride is used at a content higherthan the upper limit of the range set forth therefor, the polyimide filmcannot achieve proper levels of dielectric constant, dielectricdissipation factor, and moisture absorption rate.

Having methyl groups, which are hydrophobic, m-tolidine contributes tothe low hygroscopic property of the polyimide film. When m-tolidine isused in an amount less than the lower limit of the range, a desired lowlevel of moisture absorption rate cannot be attained.

The low moisture absorption rate attributable to m-tolidine also makes acontribution to the low dielectric dissipation factor of the polyimidefilm.

The polyimide film may a block copolymer composed of two or more blocksand particularly two blocks.

In the method for manufacturing a polyimide film according to thepresent disclosure, the thermosetting step is carried at a temperatureof 450-520° C. for 3 minutes (exclusive) to 6 minutes (inclusive).

In addition, when the thermosetting time is less than 3 minutes, thepolyimide film increases in all moisture absorption rate, the dielectricdissipation factor, and optical transmittance. For a thermosetting timelonger than 6 minutes, the film is carbonized at the surface thereof andincreases in dielectric dissipation factor, failing to attain desiredproperties.

For the thermosetting, an IR-curing furnace may be used.

In the present disclosure, the polymerization methods for polyamic acidstated above is defined as random polymerization methods. The polyimidefilm manufactured from the polyamic acid prepared in the aforementionedprocesses may be preferably applied in light of maximizing the presentdisclosure's effect of decreasing dielectric dissipation factor (Df) andmoisture absorption rate in the polyimide film.

However, the polymer chains prepared by the polymerization methodsdescribed in the foregoing have relatively short repeating units andthus are insufficient to exhibit excellent properties that the polyimidechains derived from dianhydride component retain. Preferably availablein the present disclosure may thus be a block polymerization method.

So long as it can dissolve polyamic acid, any solvent for use inpolyamic acid synthesis can be used without limitations. Preferred is anamide-based solvent.

In detail, the solvent may be an organic polar solvent, particularly apolar aprotic solvent. For example, the solvent may be at least oneselected from the group consisting of N,N-dimethylformamide (DMF),N,N-dimethylacetamide, N-methyl-pyrrolidone (NMP), gamma butyrolactone(GBL), and diglyme, but with no limitations thereto. The solvents may beused alone or in combination, as necessary.

In particular some embodiments, the solvent may includeN,N-dimethylformamide and N,N-dimethylacetamide.

Moreover, with the aim of enhancing various properties of the film, suchas slidability, thermal conductivity, corona resistance, loop hardness,etc., a filler may be added in the polyamic acid preparation processes.Particular limitations are not imparted to the filler added. Examples ofthe filler include silica, titanium oxide, alumina, silicon nitride,calcium hydrogen phosphate, calcium phosphate, and mica.

The particle diameter of the filler is not particularly limited, but isdetermined according to desirable properties of the film and types ofthe filler to be added. Generally, the filler has a mean particlediameter of 0.05 to 100 μm, particularly 0.1 to 75 μm, more particularly0.1 to 50 μm, even more particularly 0.1 to 25 μm.

When fillers have a particle diameter less than the lower limit of therange, modification effects thereof are little obtained. With a particlediameter exceeding the upper limit of the range, the fillers may greatlydegrade the surface property or mechanical property.

The amount of the filler is not particularly limited, but may bedetermined according to desirable properties of the film and particlesizes of the filler. Generally, the filler is used in an amount of 0.01to 100 parts by weight, particularly 0.01 to 90 parts by weight, andmore particularly 0.02 to 80 parts by weight, based on 100 parts byweight of the polyimide film.

When the filler is used in an amount less than the lower limit of therange, modification effects thereof are little obtained. When used in anamount higher than the upper limit of the range, the filler is apt togreatly damage mechanical properties of the film. So long as it is knownin the art, any method of adding the filler may be used withoutparticular limitations.

The polyimide film manufactured by the manufacturing method may have amoisture absorption rate of 0.3% or less and a dielectric dissipationfactor of 0.003 or less.

In a particular embodiment, the polyimide film may have a moistureabsorption rate of 0.27% or less and a dielectric dissipation factor of0.0028 or less.

Moreover, the polyimide film manufactured by the manufacturing methodmay have an optical transmittance of 25% or less.

In a particular embodiment, the polyimide film may have an opticaltransmittance of 22% or less.

In this regard, not only can the polyimide film meeting all thedielectric dissipation factor (Df), the glass transition temperature,and the moisture absorption rate be used as an insulation film forflexible metal clad laminates, but also the flexible metal dad laminatesprepared therewith can guarantee insulation stability and minimizesignal propagation delay even when they are used in electrical signaltransfer circuits for transferring signals at a frequency of 10 GHz orhigher.

A polyimide film that meets the conditions set in the foregoing has notyet been known. Below, dielectric dissipation factor (DF) and moistureabsorption rate will be elucidated in detail.

<Dielectric Dissipation Factor>

As used herein, the term “dielectric dissipation factor” means thedegree of electrical energy loss by a dielectric substance (orinsulator) as a result of the change of the electrical energy in theinsulator to heat energy by vibration of the molecules when analternating current field is applied thereto.

A value of dielectric dissipation factor is an index of the easiness ofcharge loss (dielectric loss) and is typically used as a standard forthe degree of electrical loss. With a higher dielectric dissipationfactor, an insulator is more prone to losing charges. On the other hand,the lower the dielectric dissipation factor is, the less the charges arelikely to be lost. That is, the dielectric dissipation factor explainshow much electrical loss occurs. Thus, given a low dielectricdissipation factor, the signal propagation delay attributable toelectrical energy loss is relieved, with the resultant maintenance of afast communication speed.

This condition is strongly demanded for a polyimide film used as aninsulation film. The polyimide film according to the present disclosuremay have a dielectric dissipation factor of 0.003 or less under a veryhigh frequency, such as 10 GHz.

<Moisture Absorption Rate>

The moisture absorption rate is a ratio of the moisture contained in amaterial. As a rule, a high moisture absorption rate is known to lead toan increase in dielectric constant and dielectric dissipation factor.

Water has a dielectric constant of 100 or higher in the solid state,about 80 in the liquid state, and 1.0059 in the vapor state.

That is, after being absorbed into a polyimide film, water vapor existsin a liquid state, thereby exceptionally increasing the dielectricconstant and dielectric dissipation factor of the polyimide film.

Even a trace amount of water, if absorbed, can greatly change thedielectric constant and dielectric dissipation factor in the polyimidefilm.

The polyimide film according to the present disclosure may have amoisture absorption rate of 0.3% by weight. The attainment of such a lowmoisture absorption rate is attributed to the configurationalcharacteristics of the polyimide film according to the presentdisclosure.

The non-polar moiety in the molecular structure of the polyimide filmaccording to the present disclosure is considered to be responsible forthe low moisture absorption rate.

The present disclosure provides a multilayer film comprising thepolyimide film and a thermoplastic resin layer, and a flexible metalclad laminate comprising the polyimide film and an electricallyconductive metal foil.

As the thermoplastic resin layer, for example, a thermoplastic polyimideresin layer may be available.

As stated in the foregoing, the polyimide film according to the presentdisclosure satisfies all the conditions set forth above and as such,cannot only be used as an insulation film for flexible metal cladlaminates, but also can guarantee insulation stability and minimizesignal propagation delay even at a high frequency.

No particular limitations are imparted to the metal foil used. For usein the flexible metal clad laminate of the present disclosure which isapplied to electronic or electric devices, the metal foil may include,for example, copper or a copper alloy, stainless steel or an alloythereof, nickel or nickel alloy (inclusive of 42 alloy), or aluminum oran aluminum alloy.

Flexible metal dad laminates usually employ copper foil such as rolledcopper foil, electrolytic copper foil, etc. In this disclosure, copperfoil may also be employed. In addition, the copper foil may be coatedwith an anti-corrosive layer, a heat resistance layer, or an adhesivelayer.

In the present disclosure, the metal foil is not limited to particularthicknesses, but should be thick enough to exhibit a sufficientperformance according to its use.

The flexible metal clad laminate according to the present disclosure mayhave a structure in which a metal foil is laminated on one surface ofthe polyimide film or on a thermoplastic polyimide containing adhesivelayer attached to one surface of the polyimide film.

Also, the present disclosure provides an electronic part comprising theflexible metal clad laminate as an electrical signal transfer circuit.The electrical signal transfer circuit may transfer signals at afrequency of at least 2 GHz, particularly at least at a frequency of atleast 5 GHz, and more particularly at a frequency of at least 10 GHz.

The electronic part may include, for example, a communication circuitfor mobile terminals, computers, and aerospace flights, but is notlimited thereto.

Mode for Carrying Out the Invention

Below, a better understanding of the present disclosure may be obtainedvia the following examples which are set forth to illustrate, but arenot to be construed as limiting, the present disclosure.

EXAMPLE 1

To a 500-ml reactor equipped with a stirrer and nitrogenintroduction/release tubes was input NMP while introducing nitrogenthereto. After the temperature of the reactor was set to be 30° C., adiamine component including 70% by mole of m-tolidine, 15% by mole ofpara-phenylene diamine, and 15% by mole of 4,4′-oxydianiline and an aciddianhydride component including 40% by mol of3,3′,4,4′-biphenyltetracarboxylic anhydride and 60% by mole ofpyromellitic dianhydride were input. After being observed to becompletely dissolved, the components were stirred for 120 minutes in anitrogen atmosphere, while heating to 40° C., to afford a polyamic acidhaving a viscosity of 200,000 cp at 23° C.

To the polyamic acid (PAA) solution, 1 molar equivalent of isoquinoline(IQ), which is an imidizing catalyst, was added, together with 2 molarequivalents of acetic anhydride and DMF.

Afterwards, using a spin coater, a glass substrate was coated with thedegassed polyimide precursor composition and dried at 120° C. for 30minutes in a nitrogen atmosphere to give a gel film. This gel film wasimidized by thermosetting for 5 minutes at 500° C. in an IR furnace toafford a polyimide film.

Subsequently, the polyimide film was released from the glass substrateby dipping into distilled water. The polyimide film thus manufacturedwas 15 μm thick as measured by an electric Film thickness tester(Anritsu)

Examples 2 and 3 and Comparative Examples 1 to 8

Polyimide films were manufactured in the same manner as in Example 1,with the exception that the molar equivalent of acetic anhydride and thethermosetting time were changed as shown in Table 1, below.

TABLE 1 IQ (vs. AA (vs. Thermosetting No. PAA ratio) PAA ratio) time(min) Ex. 1 1 2 5 Ex. 2 1 2.4 5 Ex. 3 1 2.8 5 C. Ex. 1 1 1.6 5 C. Ex. 21 3.4 5 C. Ex. 3 1 1.6 3 C. Ex. 4 1 2 3 C. Ex. 5 1 2.4 3 C. Ex. 6 1 2.83 C. Ex. 7 1 3.4 3 C. Ex. 8 1 2 7

<Test Example 1> Assay for Dielectric Dissipation Factor, MoistureAbsorption Rate, and Optical Transmittance

Each of the polyimide films manufactured in Examples 1 to 3 andComparative Examples 1 to 8 was measured for dielectric dissipationfactor, moisture absorption rate, and optical transmittance, and theresults are summarized in Table 2, below.

(1) Measurement of Dielectric Dissipation Factor

After the flexible metal dad laminates were left for 72 hours, thedielectric dissipation factor (Df) was measured using the impedanceanalyzer Agilent 4294A.

(2) Measurement of Moisture Absorption Rate

A moisture absorption rate was measured according ASTMD 570. In thisregard, a specimen was made by cutting the polyimide film into a squaredimension of 5 cm×5 cm and dried for 24 hours in an oven maintained at50° C. before being weighed. Then, the specimen was immersed in water at23° C. for 24 hours and weighed. The difference in weight was expressedas %.

(3) Measurement of Optical Transmittance

Using a UV spectrophotometer (Varian, Cary100), mean opticaltransmittance at 380-780 nm was measured.

TABLE 2 Moisture Optical Absorption Transmittance No. Df Rate (%) (%)Note Ex. 1 0.0024 0.21 18 — Ex. 2 0.0026 0.25 19 — Ex. 3 0.0028 0.27 22— C. Ex. 1 — — — unable to form film C. Ex. 2 0.0035 0.37 27 — C. Ex. 3— — — unable to form film C. Ex. 4 0.0035 0.37 27 — C. Ex. 5 0.0038 0.4229 — C. Ex. 6 0.0038 0.44 30 C. Ex. 7 0.0040 0.47 32 C. Ex. 8 0.00520.63 35

As seen in Table 2, all of the polyimide films manufactured in theExamples of the present disclosure exhibited significantly lowdielectric dissipation rates of less than 0.003 and moisture absorptionrates of 0.3 or less.

In addition, the films were all measured to have an opticaltransmittance of 25% or less.

It is understood that the results are attributed to the components andcomposition ratios (inter alia, dehydrating agent and imidizingcatalyst) specified in this disclosure and contents of individualcomponents play critical roles.

On the other hand, the polyimide films of Comparative Examples 1 to 8which are different in component from the Examples were measured to behigher in terms of all dielectric dissipation factor, moistureabsorption rate, and optical transmittance than those of the Examples.Therefore, the polyimide films of Comparative Examples are predicted tobe difficult to use in electronic parts in which signal transmission isperformed at a high frequency in gigabytes.

Although the present disclosure has been described with reference to theembodiments thereof, it should be understood by those skilled in the artthat various applications and modifications may be made withoutdeparting from the scope of the present disclosure.

INDUSTRIAL APPLICABILITY

The present disclosure provides a polyimide film composed of specificcompositions of specific components and a manufacturing method therefor.With low dielectric, low hygroscopic, and low optical transmittanceproperties in combination, the polyimide can find advantageousapplications in various fields demanding such properties, especiallyelectronic parts such as flexible metal clad laminates, etc.

1. A method for manufacturing a polyimide film, the method comprisingthe steps of: preparing a polyamic acid solution; preparing a polyamicacid composition by adding 2-3 mole equivalents of a dehydrating agentto the polyamic acid solution; and applying the polyamic acid to asupport to form a film, followed by thermosetting the film in a heater.2. The method of claim 1, wherein an imidizing catalyst is additionallyadded in an amount of 0.5-2 mole equivalents to the polyamic acidsolution in the step of preparing a polyamic acid composition.
 3. Themethod of claim 1, wherein the polyamic acid solution contains: an aciddianhydride component including 3,3′,4,4′-biphenyltetracarboxylicdianhydride (BPDA), and pyromellitic dianhydride (PMDA); and a diaminecomponent including m-tolidine, 4,4′-oxydianiline (ODA), andp-phenylenediamine (PPD).
 4. The method of claim 3, wherein3,3′,4,4′-biphenyltetracarboxylic dianhydride is used at a content of30% by mole to 50% by mole and pyromellitic dianhydride is used at acontent of 50% by mole to 70% by mole, based on a total of 100% by moleof the acid dianhydride component,
 5. The method of claim 3, whereinm-tolidine is used at a content of 60% by mole to 80% by mole for,p-phenylenediamine is used at a content of from 10% by mole to 25% bymole, and 4,4′-oxydianiline (ODA) is used at a content of from 10% bymole to 25% by mole, based on a total of 100% by mole of the diaminecomponent.
 6. The method of claim 1, wherein the dehydrating agent isacetic anhydride.
 7. The method of claim 2, wherein the imidizingcatalyst is at least one selected from the group consisting ofisoquinoline, β-picoline, pyridine, imidazole, 2-imidazole,1,2-dimethylimidazole, 2-phenylimidazole, and benzimidazole.
 8. Themethod of claim 1, wherein the thermosetting is carried out at 450-520°C. for 3 minutes (exclusive) to 6 minutes (inclusive).
 9. The method ofclaim 1, wherein the polyimide film comprises a copolymer composed oftwo or more blocks.
 10. A polyimide film, manufactured by the method ofclaim
 1. 11. The polyimide film of claim 10, wherein the polyimide filmhas a moisture absorption rate of 0.3% or less and a dielectricdissipation factor (Df) of 0.003 or less.
 12. The polyimide film ofclaim 10, wherein the polyimide film has an optical transmittance of 25%or less.
 13. A multilayer film, comprising the polyimide film of claim10 and a thermoplastic resin layer.
 14. (canceled)
 15. (canceled)